1. Department of Microbiology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada, Department of Fisheries and Oceans, Central and Arctic Region, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada, Flett Research Ltd., 440 DeSalaberry Avenue, Winnipeg, Manitoba R2L 0Y7, Canada, and Department of Geography, McGill University, Burnside Hall, 805 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada